Various techniques have been utilized to remove sulfur dioxide from gas streams. For example, on an industrial basis, waste gases have been passed through a metal oxide medium in a sulfur oxide retention zone at a temperature in which the sulfur oxides are sorbed onto the medium. Thereafter, the medium may be regenerated by heating to a temperature at which the sulfur oxides are released. One such system is described in D'Souza et al U.S. Pat. No. 4,233,276. A survey of various metal oxides suitable for the above purpose is set out in Lowell et al, "Selection of Metal Oxides for Removing SO.sub.2 from Flue Gas", Ind. Eng. Chem. Process Des. Develop., Vol. 10, No. 3, 1971, pp. 384-390. This article concludes that the most promising oxides are Al, Bi, Ce, Co, Cr, Cu, Fe, Hf, Ni, Sn, Th, Ti, V, U, Zn, and Zr.
In an analytical environment, the sulfur content of carbonaceous samples have been determined by gas chromatography followed by sulfur dioxide analysis, such as in a conductivity cell. In Cropper U.S. Pat. No. 4,120,659, the sample is combusted to form sulfur dioxide and then passed through a gas chromatography column in which the sulfur dioxide is separated on a packing comprising a silica gel at a first temperature on the order of 100.degree. C. A carrier gas sweeps the column and passes the gases to the conductivity detector for analysis.
Another system for the analysis of sulfur has been suggested in Oita, I. J., "Determination of Sub-ppm Levels of Sulfur", Abstract 119, American Chemical Society, Las Vegas, Nev. Meeting (Aug. 27, 1980). There, the sulfur in liquids or solids is analyzed by combustion of the sample to form a sulfur dioxide-containing analysis stream, which is passed through a copper oxide trapping medium at 700.degree. C. to trap the sulfur pyrolysis products as copper sulfate. After completion of combustion, the copper sulfate is heated to 900.degree. C. to release the sulfur as sulfur dioxide.
The Oita system is subject to a number of disadvantages. At the temperature of sulfur oxide release, both sulfur dioxide and sulfur trioxide are formed in the oxygen-containing combustion gas which passes through the combustion zone. Thus, it is necessary to assume a certain ratio of sulfur dioxide to sulfur trioxide in order to calculate the sulfur content of the sample. It has been found that this ratio is about 50% and is not reproducible, leading to errors in analysis.